The contractor's objective is to detect blood units infectious for cytomegalovirus (CMV) by using the relatively new technique of in situ hybridization with cloned, biotinylated segments of CMV DNA. The signal will then be identified using a non-radioactive enzyme probe. The system will be optimized using CMV-infected human fibroblasts. Further testing using blood "spiked" with infected cells will be performed to determine the effect of blood/blood cells on signal detection. The final step in developing the assay will be to test actual specimens and compare to results obtained by standard culture techniques.